Nonimpact printers in general utilize either electrostatic or thermal print elements called styli or nibs, which when activated produce a mark on paper or other print media running across the printhead. One type of printhead utilizing staggered rows of nibs and glass, porcelain, or ceramic substrates is illustrated in U.S. Pat. No. 3,578,946. Printheads of this type utilize substrates made out of hard materials to prevent erosion of the printhead with use. These printheads are in general very short in length, and their manufacture in lengths over, for instance, 12 inches, is exceedingly difficult due to the delicate nature of the substrate material. Because the materials are delicate, breakage in fabrication often precludes the ability to fabricate large-scale printheads. These printheads are useful, for instance, in cartography, printed circuit layout printing, hard-copy line plots for LSI designing, CAD/CAM plots, and large-scale sonar surveillance charting.
While large-scale printheads have been made in the past with wires potted in epoxy, these large-scale printheads suffer dramatically from wear due to the low wear resistance of the epoxy potting compound. These printheads also suffer from resolution problems commensurate with the ends of the wires which are cut off after being embedded in plastic. The poor wear characteristics of the prior art potted printheads aside, resolution of at most 50-100 lines per inch is all that is available using wire-potting techniques. While wire-potting does permit manufacture of large-scale printheads, none can approach magazine quality of 200-400 lines per inch, or indeed such detail as would be afforded by a system which can produce 800-1000 lines per inch, such as the subject system which will be described hereinafter.
While it might have been thought that in order to achieve an elongated printhead, all that would have to be done would be to butt shorter printheads together, this is impractical. First, the butting process is one involving finished printheads. By chamfering or obliquely slicing finished printheads through sawcutting, polishing, and the like, many finished printheads will be damaged, and the cost of such a process is increased by the resulting decreased yield. Assuming that one were successful in fashioning the buttable short printheads, the finished printhead would have butting lines or crevices across it which would entrap fibers of paper or other types of contamination in the printer itself. Also the printhead would wear unevenly at the crevices, so that the mere butting together of short printheads is both economically unfeasible and results in a printhead which entraps fibers and which wears unevenly.
It will be appreciated that in the normal printhead configuration, rows of printing styli or nibs are packed relatively close together such that the spacing between one row of styli and another row of styli is typically on the order of 10 mils. In order to accomplish the 10-mil spacing between rows of styli, it is important that the substrate bearing the styli be relatively thin. The thinness of the substrates on which the styli are patterned presents insurmountable manufacturing problems when attempting to obtain and handle long, very fragile, thin substrates. It should be noted that the shorter the printhead substrate, the less prone it is to breakage. Each long broken substrate represents the breakage of a costly completed substrate having a row of styli or nibs interconnected with patterned bus structures, sometimes involving the use of thru-holes which run through the thin, fragile substrate. The yield for thru-holed thin substrates is low, and additional breakage during patterning and subsequent handling makes a successfully completed substrate a valuable commodity. If these valuable completed substrates are then to be cut and butted, further damage to completed substrates can occur which results in the loss of a complex costly part.